Tip rub of the airfoil tip with the compressor casing causes detrimental effects, such as high loads transferred to the root of the airfoil, high heat transmitted to the airfoil blade material, which results in fatigue debit, and micro-cracking of the airfoil. Attempts to reduce efficiency debit from large clearances between the airfoil tip and casing, such as by providing abradable casings of case liners and oversized seals have been somewhat unsuccessful because these methods are subject to limitations such as complex repair procedures necessary to access the abradable case liner.
A rotatable component, coating and method of coating the rotatable components for engines that do not suffer from the above drawbacks is desirable in the art.